Known methods for making plastic pellets and organic rubber pellets are not generally applicable to the pelletization of silicone rubber. Pelletized forms of silicone rubber are very useful because they can be fed to extrusion devices for coating electrical wires with silicone rubber insulations, without the need to cut sheets or plates of the composition into small strips, as is done conventionally. It is difficult, because of its inherent weak consistency, to pelletize silicone rubber, and most attempts produce irregular shaped granules which tend either to stick together or not to flow freely during packaging and use.
French Pat. No. 1,567,578 describes one way of providing silicone rubber pellets. This is a generally two step method in which the sheet of silicone rubber composition is cut into ribbons and then the ribbons are cross-cut into "pastilles." Both operations are carried out in an "atmosphere" of a pulverizing agent, such as talc. In addition to requiring a complicated apparatus having a first and a second cutting element, the process of the French patent produces the silicone rubber in the form of approximately cubical, and preferably regular form cubes or balls, called "pastilles." The cubical form has sharp edges and tends not to flow freely in extruder hoppers.
It has now been discovered that if silicone rubber compositions are coated as they are extruded into strands, and the strands are comminuted in a chamber filled with a dust fog or cloud of particulate agent for coating the pellets, before contact is made with other strands, and the pellets are completely encapsulated in dust before they are chopped from the strands, a superior product is provided, in only one step, and, with careful attention to maintaining critical size and shape, a novel cylindrical pellet is produced which has no tendency to "log-jam" in the extruder hopper.